SEARCH · PubMed Health

Results for “Polymers”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources

PubMed2000

Polymer-based materials to be used as the active element in microsensors: a scanning force microscopy study

Polymer-based materials can be incorporated as the active sensing elements in chemiresistor devices. Most of these devices take advantage of the fact that certain polymers will swell when exposed to gaseous analytes. To measure this response, a conducting material such as carbon black is incorporated within the nonconducting polymer matrix. In response to analytes, polymer swelling results in a measurable change in the conductivity of the polymer/carbon composite material. Arrays of these sensors may be used in conjunction with pattern recognition techniques for purposes of analyte recognition and quantification. We have used the technique of scanning force microscopy (SFM) to investigate microstructural changes in carbon-polymer composites formed from the polymers poly (isobutylene) (PIB), poly (vinyl alcohol) (PVA), and poly (ethylene-vinyl acetate) (PEVA) when exposed to the analytes hexane, toluene, water, ethanol, and acetone. Using phase-contrast imaging (PI), changes in the carbon nanoparticle distribution on the surface of the polymer matrix are measured as the polymers are exposed to the analytes in vapor phase. In some but not all cases, the changes were reversible (at the scale of the SFM measurements) upon removal of the analyte vapor. In this paper, we also describe a new type of microsensor based on piezoresistive microcantilever technology. With these new devices, polymeric volume changes accompanying exposure to analyte vapor are measured directly by a piezoresistive microcantilever in direct contact with the polymer. These devices may offer a number of advantages over standard chemiresistor-based sensors.

Journal Article↗

PubMed1993

High resolution fractionation and characterization of ADP-ribose polymers.

Methods are described for the high resolution fractionation and characterization of ADP-ribose polymers. Polymers prepared in vitro using purified poly(ADP-ribose) polymerase were isolated free from interfering nucleic acids and salts using dihydroxyboronyl-Bio-Rex 70 chromatography and fractionated using anion exchange high-pressure liquid chromatography. The homogeneity of isolated polymer fractions was characterized by gel electrophoresis and polymer size was determined by analysis following enzymatic digestion to nucleosides. The method allows isolation of oligomers up to 50 mer as single species and larger polymers can be isolated free from oligomers according to size and branching frequency. The ability to isolate individual species of ADP-ribose polymers should prove useful for the study of the polymers and their noncovalent interactions with other components of chromatin. Microheterogeneity of individual oligomers was studied and shown to be due to differences at the protein proximal ends resulting from the chemical method of release of polymers from protein. The method also was applied to fractionate polymers generated in intact cultured mouse cells in response to treatment with the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine.

Animals↗

PubMed1996

Collagen synthesized in fluorocarbon polymer implant in the rabbit cornea.

The integration of microporous polymer into tissues is of great interest for the production of keratoprosthetic devices. Our previous studies showed functional differentiated cells and collagen synthesis in the pore of an expanded polytetrafluoroethylene implant. This study identifies and quantifies collagen types synthesized in the implant. Expanded polytetrafluoroethylene polymers were implanted in the rabbit corneas. The collagen extracted from the polymer and implanted stroma after 1, 3 and 6 months was quantified by measuring hydroxyproline. The relative proportions of collagen types were determined by densitometric analysis after SDS-PAGE. The collagen-to-protein ratio in the polymer increased from 0.22 to 0.70 between the first and third month after implantation becoming similar to control cornea. So that of the protein and collagen densities in the polymer and implanted stroma were similar to the control from the third month. The collagen synthesized in the polymer was mainly type I (87%) plus a small amount of type III (8%) 1 month after implantation. The collagen distribution from the third month after implantation was similar to that of the controls and remained constant thereafter in the polymer implant and in the implanted stroma. Immunogold labelling techniques confirmed these results. Implantation of this PTFE disc induced no obvious modification of the corneal stroma, confirming that this polymer is a good interface that is compatible with the native corneal stroma. The keratocytes in this polymer rapidly adopted a corneal phenotype, distinct from the dermal or scaring phenotype as shown by the collagen types produced in the implant.

Animals↗

PubMed1997

Motion of a Colloidal Particle Coated with a Layer of Adsorbed Polymers in a Spherical Cavity

An analytical study is presented for the quasisteady translation and steady rotation of a spherical particle covered by a layer of adsorbed polymers located at the center of a spherical cavity that may also have an adsorbed polymer layer on its inside wall. The Reynolds number is assumed to be small, and the surface polymer layers are assumed to be thin with respect to the particle radius and the spacing between solid surfaces. To solve the Stokes flow equations within and outside the polymer layers a method of matched asymptotic expansions in small parameters lambda1 and lambda2 is used, where lambda1 and lambda2 are the ratios of the polymer-layer length scale to the radius of curvature at the particle surface and at the cavity wall, respectively. The results for the hydrodynamic force and torque exerted on the particle are expressed as an effective hydrodynamic thickness (L) of the adsorbed polymer layer surrounding the particle, which are accurate to O(lambda21). The O(lambda1) term for L normalized by its value in the absence of the cavity is found to be independent of the polymer segment distribution, the hydrodynamic interactions among the segments, and the volume fraction of the segments. The O(lambda21) term for L, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant in appropriate situations.

Journal Article↗

PubMed1997

Interaction between Cetyl Pyridinium Chloride and Water-Soluble Polymers in Aqueous Solutions

The interaction between cetyl pyridinium chloride and different-molecular-weight poly(vinylpyrrolidone) (PVP) and poly(ethylene glycol) (PEG) polymers has been investigated by means of electrical conductivity and fluorescence probing. No interaction between the low-molecular-weight PVP polymers and the surfactant was detected, whereas a significant interaction was observed between high-molecular-weight PVP polymers or PEG polymers and cetyl pyridinium chloride. The results indicate that polymer-surfactant aggregates start to form at a surfactant concentration higher than the critical micelle concentration of micelles without polymers. In contrast, the degree of ionization and the interface polarity decrease as compared with values of micelles without polymers. The Gibbs free energy associated with the interaction was also calculated. The values show that the addition of polymers stabilizes polymer-surfactant aggregates. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗

PubMed1997

Effects of Adsorbed Polymers on the Axisymmetric Motion of Two Colloidal Spheres

The effects of adsorbed polymer on the slow motion of two spherical particles along the line of their centers are examined semianalytically. The particles may have unequal radii, and their surface polymer layers are allowed to differ in characteristics. The surface polymer layer on each particle is assumed to be thin relative to the radius of the particle and to the surface-to-surface distance between the particles. A method of matched asymptotic expansions in small parameters lambdai (where i = 1 and 2) combined with a boundary collocation technique is used to find the solution for the creeping flow field within and outside the adsorbed polymer layers, where lambdai is the ratio of the polymer-layer length scale to the radius of particle i. The results for the hydrodynamic forces exerted on the particles in a resistance problem and for the particle velocities in a mobility problem are expressed in terms of the effective hydrodynamic thicknesses (Li) of the polymer layers, which are accurate to O(lambdai2). The O(lambdai) term for Li normalized by its value in the absence of the other particle is found to be independent of the polymer segment distribution, the hydrodynamic interactions among the segments, and the volume fraction of the segments. The O(lambdai2) term for Li, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the effects of particle interactions on the motion of polymer-coated particles can be quite significant, especially when the particles are moving in the opposite directions. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗

PubMed1997

Optimizing interstitial delivery of BCNU from controlled release polymers for the treatment of brain tumors.

Two approaches for improving the interstitial administration of carmustine (BCNU) using 3.8% loaded poly(carboxyphenoxypropane-sebacic acid), an implantable biodegradable anhydride which significantly prolongs survival in patients with recurrent malignant gliomas, were evaluated. First, increasing the ratio of carboxyphenoxypropane (CPP) to sebacic acid (SA) in the polymer increases its hydrolytic stability, thus prolonging its half-life in vivo, and extending the period of drug release. A second approach is to increase the dose of drug loaded into the polymer. This study evaluated the relative merits of these two approaches by comparing release kinetics, safety, and efficacy of escalating BCNU does in polymers with 20:80 and 50:50 ratios of CPP to SA. At the highest dose tested, the 50:50 polymer released BCNU 2.5 times as long in vitro as the 20:80 polymer. Both formulations were nontoxic in rat brains for all BCNU doses tested except 32%. The 20:80 and 50:50 polymers were equally effective in the rat intracranial 9L-glioma model. A dose-response relationship for BCNU was observed (hazard ratio 0.8354 for each mg/kg increase, P < 0.001). The two highest loading doses of BCNU improved survival 40-fold (P < 0.001). The 20% BCNU-loaded 20:80 polymer achieved the best balance of toxicity and antitumor efficacy, yielding a 75% long-term survival rate. Further evaluation of this polymer in monkeys suggests that it might be used with acceptable toxicity. This study establishes that a dose-escalation strategy for improving BCNU controlled-release polymers is more effective than adjusting the ratio of CPP to SA to prolong drug release.

Animals↗

PubMed2004

Nucleation of calcium oxalate crystals on an imprinted polymer surface from pure aqueous solution and urine.

Calcium oxalate (CaOx) is the most common component of human kidney stones. Heterogeneous nucleation is regarded as the key mechanism in this process. In this study, we have used an imprinted 6-methacrylamidohexanoic acid/divinylbenzene co-polymer as a biomimetic surface to nucleate CaOx crystal formation. The polymer was imprinted with either calcium oxalate monohydrate (COM) or dihydrate (COD) template crystals. These were washed out of the polymer, which was then immersed in various test solutions. The test solutions were an aqueous solution of calcium chloride and sodium oxalate, artificial urine and a sample of real urine. Crystals that formed on the polymer surface were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, atomic absorption spectroscopy and scanning electron microscopy. Results showed that in the aqueous solution the COM-imprinted polymer induced the nucleation of COM. The COD-imprinted polymer induced only trace amounts of COD crystallization, together with larger quantities of COM. In artificial and real urines, COM also specifically precipitated on the COM-imprinted surface. The results show that, at least to some extent, the imprinted polymers direct formation of their morphologically matched crystals. In the case of COD, however, it appears that either rapid hydrate transformation of COD to COM occurs, or the more stable COM polymorph is directly co-precipitated by the polymer. Our results support the hypothesis that heterogeneous nucleation plays a key role in CaOx stone formation and that the imprinted polymer model could provide an additional and superior diagnostic tool for stone researchers to assess stone-risk in urine.

Acrylamides↗

PubMed2004

A study of dilational rheological properties of polymers at interfaces.

Viscoelastic properties of two polymers, partially hydrolyzed polyacrylamide and partially hydrolyzed modified polyacrylamide, widely used in chemical flooding in the petroleum industry, were investigated at three interfaces, water-air, water-dodecane, and water-crude oil, by means of a dilational method provided by I.T. Concept, France, at 85 degrees C. Polymer solutions were prepared in brine with 10,000 mg/l sodium chloride and 2000 mg/l calcium chloride. It has been shown that the viscoelastic modulus increases with the increment of polymer concentration in the range of 0-1500 mg/l at the water-air interface. Each polymer shows different viscoelatic behavior at different interfaces. Generally speaking, values of the viscoelastic modulus (E), the real part (E'), and the imaginary part (E") at the crude oil-water interface for each polymer are lower than at the air-water or water-dodecane interface. The two polymers display different interfacial properties at the same interface. Polymer No. 2 gives more viscous interfaces than polymer No. 1. All the information obtained from this paper will be helpful in understanding the interfacial rheology of ultra-high-molecular-weight polymer solutions.

Journal Article↗

PubMed2005

Glycerol-l-lactide coating polymer leads to delay in bone ingrowth in hydroxyapatite implants.

Glycerol-l-lactide as coating polymer for the delivery of basic fibroblast growth factor (bFGF) from hydroxyapatite (HA) ceramic implants was shown to lead to significant delay in bone ingrowth into the implants compared to implants without the coating polymer. The purpose of this work was to study bone ingrowth in HA ceramic implants with and without the coating polymer but without growth factors to enable differentiation between a locking effect of the pores by the polymer and the fact of inactivation of the growth factors by the polymer, which could both be possible for the delay. A defect was created in the subchondral region of both femurs in 24 miniature-pigs and was either filled by the HA implants with or without the coating polymer. Histomorphometry showed a significant delay in bone ingrowth in the polymer coated implants both after 6 and 12 weeks. Detailed histology revealed that the HA pores were completely "locked" by the polymer leading to complete loss of the osteoconductive properties of the HA. Also electron microscopy showed filling of the HA pores by the polymer. Therefore, it can be concluded that glycerol-l-lactide should not be used to coat HA ceramic implants due to significant delay in bone ingrowth.

Animals↗

PubMed2006

Clinical performance of posterior metal-free polymer crowns with and without fiber reinforcement: one-year results of a randomised clinical trial.

OBJECTIVES: The aim of this study was to evaluate the clinical performance of posterior, metal-free polymer crowns with and without a glass-fiber framework, in comparison to metal-ceramic crowns. METHODS: After randomisation, 80 single crowns, manufactured from a newly designed polymer composite, were set in posterior teeth. Half of these received a glass-fiber framework, while half were prepared without any framework stabilisation. All polymer crowns were adhesively luted with resin cement. As the control group, 40 conventional metal-ceramic crowns were inserted with hybrid cement. Documentation included failures and other complications, as well as gingival/plaque status and aesthetic performance. RESULTS: During the 12-month observation period, eight polymer crowns and three metal-ceramic crowns showed clinically relevant complications. The most frequent complications were root canal treatments (n=4) and decementation (n=4) of the crowns. A total of two crowns (one polymer crown with fiber network and one crown of the control group) had to be replaced. After 12 months, polymer crowns with glass-fiber framework exhibited significantly higher plaque accumulation (p=0.005) and gingival index (p=0.04) than metal-ceramic crowns, while no significant differences could be demonstrated for polymer crowns without fiber reinforcement. Postoperative sensibility and aesthetic performance did not differ significantly between the groups. CONCLUSIONS: Within a 12-month observation period, posterior polymer crowns with and without glass-fiber framework demonstrated acceptable stability and aesthetic performance. Polymer crowns with fiber framework showed significant higher plaque accumulation and gingival index than metal-ceramic crowns.

Adult↗

PubMed2005

Evaluation of adhesion of chairside hard relining materials to denture base polymers.

STATEMENT OF PROBLEM: Removable denture bases are made of modified poly(methyl methacrylate) (PMMA), which has reliable bond strength with resins containing methyl methacrylate (MMA). However, some hard relining materials with different chemical compositions have been reported to have less than adequate bond strength to PMMA denture base polymers. PURPOSE: This in vitro study evaluated the initial bonding properties of chairside hard relining materials to different removable denture base polymers, as well as the structure of the interface. MATERIAL AND METHODS: The tensile strength (MPa) of adhesion of 8 chairside hard relining materials (Original Truliner, GC Reline Hard, Ufigel Hard, Triad Reline, New Truliner, Light Liner, Astron LC Hard, and Flexacryl Hard) was tested against 3 denture base polymers (Ivocap Plus, Paladon 65, and Palapress Vario). Dumbbell-shaped specimens with a 6-mm diameter of bonding surface were used for tensile testing of bond strength (n=5). An MMA containing hard relining material (Original Truliner) was used as a control. Tensile strength of the bond was calculated using the bonding area and maximum force under tension. Statistical analyses of data were conducted with 2-way analysis of variance (alpha=.05). The influence of the bonding agents and the relining materials on the PMMA denture base surface layer and its structure were investigated. The depths of the swollen layers were measured with a transmission light microscope. Fracture surfaces after testing were also visually evaluated. Chemical analyses of all materials prior to testing were performed using high-performance liquid chromatography. RESULTS: Significant differences were found among tensile bond strengths of chairside hard relining materials to PMMA denture base polymers forming 3 different groups (P<.001). No significant difference among different denture base polymers was found with regard to tensile strength of adhesion (P=.918), but the interaction term between hard relining material and denture base polymer was found to be significant (P<.001). The tensile bond strength of the relining materials and denture base polymers was found to range from 8% to 60% of the strength of the PMMA denture base polymers. CONCLUSION: The chemical composition of the bonding agents and the relining materials and their combinations affected the depth of the swollen layers of the denture base polymers and the tensile strength of adhesion.

Acrylic Resins↗

PubMed1999

Polymer-cushioned bilayers. I. A structural study of various preparation methods using neutron reflectometry.

This neutron reflectometry study evaluates the structures resulting from different methods of preparing polymer-cushioned lipid bilayers. Four different techniques to deposit a dimyristoylphosphatidylcholine (DMPC) bilayer onto a polyethylenimine (PEI)-coated quartz substrate were examined: 1) vesicle adsorption onto a previously dried polymer layer; 2) vesicle adsorption onto a bare substrate, followed by polymer adsorption; and 3, 4) Langmuir-Blodgett vertical deposition of a lipid monolayer spread over a polymer-containing subphase to form a polymer-supported lipid monolayer, followed by formation of the outer lipid monolayer by either 3) horizontal deposition of the lipid monolayer or 4) vesicle adsorption. We show that the initial conditions of the polymer layer are a critical factor for the successful formation of our desired structure, i.e., a continuous bilayer atop a hydrated PEI layer. Our desired structure was found for all methods investigated except the horizontal deposition. The interaction forces between these polymer-supported bilayers are investigated in a separate paper (Wong, J. Y., C. K. Park, M. Seitz, and J. Israelachvili. 1999. Biophys. J. 77:1458-1468), which indicate that the presence of the polymer cushion significantly alters the interaction potential. These polymer-supported bilayers could serve as model systems for the study of transmembrane proteins under conditions more closely mimicking real cellular membrane environments.

Adsorption↗

PubMed1997

In vitro effects of glucose polymer-containing peritoneal dialysis fluids on phagocytic activity.

Commercially available peritoneal dialysis fluids (PDFs) are known to impair peritoneal cellular defense mechanisms. We have investigated the influence of glucose polymer-containing PDFs on phagocytic function in vitro. Polymorphonuclear neutrophils (PMNLs) and monocytes (MNs) from 10 continuous ambulatory peritoneal dialysis patients and 10 healthy donors were incubated in PDFs containing either 7.5% icodextrin (glucose polymer) or 1.5% glucose at original pH and pH 7.4. Chemiluminescence response and H202 production were measured following stimulation with preopsonized Staphylococcus epidermidis or phorbol myristate acetate. Phagocytosis of radiolabeled bacteria and killing capacity of the cells were determined. A comparison of the impact of glucose polymer versus glucose-containing solutions at their original pH on the oxidative metabolism of the cells showed a highly significant difference (P < 0.0001) in favor of glucose polymers for H202 production of PMNLs (7.78 +/- 4.5 nmol cytochrome C reduction/10(6) cells/min v 1.11 +/- 0.67 nmol cytochrome C reduction/10(6) cells/min) and MNs (7.66 +/- 3.6 nmol cytochrome C reduction/10(6) cells/min v 1.29 +/- 0.86 nmol cytochrome C reduction/10(6)cells/min). Correspondingly, PMNLs and MNs incubated in glucose polymers showed a significantly higher chemiluminescence response irrespective of the stimulant used (P < 0.0001). Applying the killing assay on PMNLs also revealed a significantly higher percentage of inactivated bacteria (45.5% +/- 11.0% v 29.2% +/- 15.5%; P < 0.05). After adjustment of pH to 7.4, a significant difference could only be found for H202 production of PMNLs in favor of glucose polymers (16.73 +/- 6.98 nmol cytochrome C reduction/10(6) cells/min v 11.65 +/- 5.37 nmol cytochrome C reduction/10(6) cells/min; P < 0.05). In addition, we compared the glucose-polymer solution to an otherwise equally composed equiosmolar solution that contained 0.274% glucose instead of glucose polymers. No significant differences were detected with any of the tests applied. Our data suggest that glucose polymer solutions are comparatively less suppressive to phagocytic function than currently used glucose-containing PDFs. This effect may be attributed to the low osmolarity of these solutions.

Adult↗

PubMed2001

Crystallization of hydrocortisone acetate: influence of polymers.

The influence of hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG400) on the crystallization of hydrocortisone acetate (HA) was studied. Supersaturation was created by the cosolvent technique. Spontaneous nucleation was observed when no polymer was used as the additive. In the presence of the polymer, nucleation was delayed. The nucleation time decreased with increasing supersaturation at a particular polymer concentration and increased with increasing polymer concentration at a particular supersaturation. Habit modification from a well-defined polar prismatic morphology to a wing-shaped morphology was observed when HPMC was used as the additive. The effect of PVP and PEG400 on the morphology of HA was less pronounced compared to the cellulose polymers. The mechanism of nucleation retardation by the polymers is explained in terms of association of HA with the polymer through hydrogen bonding. The growth may be inhibited by the hydrodynamic boundary layer, in which the polymers accumulate as well as by the adsorption of the polymer onto the crystal surface. The habit modification of HA by HPMC is due to different extents of adsorption on different faces of the crystal, the extent of which is dependent on the hydrogen bonding functional groups that are exposed at each face of the crystal.

Crystallization↗

PubMedDate not supplied

Biosynthesis and properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) polymers.

In support of programs to identify polyhydroxyalkanoates with improved materials properties, we report on our efforts to characterize the mechanical and thermal properties of copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx). The copolyesters, having molar fraction of 3HHx ranging from 2.5 to 35 mol % and average molecular weights ranging from 1.15 x 10(5) to 6.65 x 10(5), were produced by fermentation using Aeromonas hydrophila and a recombinant strain of Pseudomonas putida GPp104. The polymers were chloroform extracted and characterized by solution-state and solid-state nuclear magnetic resonance (NMR) spectroscopy and a variety of mechanical and thermal tests. Solution-state (1)H NMR data were used to determine polymer composition-of-matter, while solution-state (13)C NMR data provided polymer-sequence information. Solvent fractionation and NMR spectroscopic characterization of these polymers showed that polymers containing up to 9.5 mol % 3HHx had a Bernoullian compositional distribution. By contrast, polymers containing more than 9.5 mol % 3HHx had a bimodal polymer composition. Solvent fractionation of these 3HHx-rich polyesters produced two polymer fractions, each of which was again consistent with Bernoullian polymerization statistics. Solid-state NMR relaxation experiments provided insight into aging in poly(3HB-co-3HHx) copolymers, demonstrating increased polymer-chain motion with increasing 3HHx content. The elongation-to-break ratio in the polyesters increased with increasing molar fraction of 3HHx monomers. Aging properties of the poly(3HB-co-3HHx) copolymers were very similar to copolymers of 3HB and 3-hydroxyvalerate (3HV). However, poly(3HB-co-3HHx) exhibited increased activation energy to thermal degradation with increasing 3HHx content.

3-Hydroxybutyric Acid↗

PubMed2005

Density-functional study of interfacial properties of colloid-polymer mixtures.

Interfacial properties of colloid-polymer mixtures are examined within an effective one-component representation, where the polymer degrees of freedom are traced out, leaving a fluid of colloidal particles interacting via polymer-induced depletion forces. Restriction is made to zero-, one-, and two-body effective potentials, and a free energy functional is used that treats colloid excluded volume correlations within Rosenfeld's fundamental measure theory, and depletion-induced attraction within first-order perturbation theory. This functional allows a consistent treatment of both ideal and interacting polymers. The theory is applied to surface properties near a hard wall, to the depletion interaction between two walls, and to the fluid-fluid interface of demixed colloid-polymer mixtures. The results of the present theory compare well with predictions of a fully two-component representation of mixtures of colloids and ideal polymers (the Asakura-Oosawa model) and allow a systematic investigation of the effects of polymer-polymer interactions on interfacial properties. In particular, the wall surface tension is found to be significantly larger for interacting than for ideal polymers, whereas the opposite trend is predicted for the fluid-fluid interfacial tension.

Journal Article↗

PubMed2006

Synthesis and characterization of long perylenediimide polymer fibers: from bulk to the single-molecule level.

The synthesis and characterization of perylenediimide polyisocyanides is reported. In addition to short oligomers, our synthetic approach results in the formation of extremely long, well-defined, and rigid perylenediimide polymers. Ordering and close-packing of the chromophores in these long polymers is guaranteed by attachment to a polyisocyanide backbone with amino acid side chains. Hydrogen bonding interactions between those groups stabilize and rigidify the helical polymer structure. The rodlike nature of the synthesized long perylenediimide pendant polyisocyanides as well as the helical arrangement of the chromophores is demonstrated by means of atomic force microscopy. Remarkably, polymer fibers up to 1 mum in length have been visualized, containing several thousands of perylenediimide molecules. Circular dichroism spectroscopy reveals the chiral organization of the chromophore units in the polymer, whereas absorption and emission measurements prove the occurrence of excited-state interactions between those moieties due to the close packing of the chromophore groups. However, an intricate optical behavior is encountered in bulk as a result of the coexistence of short oligomers and long polymers of perylenediimide, a situation subsequently uncovered by means of single-molecule experiments. Individual long helical perylenediimide polyisocyanides exhibit a typical red-shifted fluorescence spectrum, which, together with depolarized emission continuously decreasing in time, demonstrate that fluorescence arises from multiple excimer-like species in the polymer. Upon continuous irradiation of these long polymers, a fast decay in fluorescence lifetime is observed, a situation explained by photoinduced creation of quenching sites. Radical/ion formation by intramolecular electron transfer between close-by perylenediimide moieties is the most probable mechanism for this process. Appropriate control of the electron-transfer process might open the possibility of applying these polymers as perylenediimide-based supramolecular nanowires.

Anisotropy↗