Structural Characterization and Degradability of Poly(L‐lactic acid)s Incorporating Phenyl‐Substituted α‐Hydroxy Acids as Comonomers

Three types of copolymers of poly(L ‐lactic acid) (PLLA) were synthesized by direct polycondensation of L ‐lactic acid and phenyl‐substituted α‐hydroxy acids (L ‐phenyllactic acid and D ‐ and L ‐mandelic acids). It was found that the glass transition temperature of the copolymers comprising L ‐mandelic acid became significantly higher (from 58 to 69 °C) with increasing content of L ‐mandelic acid (from 0 to 50 mol‐%) although the M _w decreased (from 87 000 to 4 000 Da). The cast films of the L ‐mandelic acid containing copolymers showed improved tensile properties compared with those of the PLLA film. This may be due to a pinning effect of the L ‐mandelic acid units on the helix formation of PLLA, although 30% of the units were racemized. The enzymatic degradability of the L ‐mandelic acid containing copolymers was much higher than that of PLLA, as analyzed with Proteinase K® originating from Tritirachium album.

Synthesis of copolymers of L ‐lactic acid and phenyl‐substituted α‐hydroxy acids.     

Highly Efficient and Well‐Controlled Ambient Temperature RAFT Polymerization under Solar Radiation

Highly efficient and well‐controlled ambient temperature reversible addition–fragmentation chain transfer (RAFT) polymerization is readily carried out under environmentally friendly mild solar radiation. This discovery has significantly extended studies from man‐made separated‐spectroscopic‐emission UV‐vis radiation (Macromolecules 2006 , 39, 3770) to natural continuous‐spectroscopic‐emission solar radiation for ambient temperature RAFT polymerization.

     

Synthesis and Thin Film Phase Behaviour of Functional Rod‐Coil Block Copolymers Based on Poly(para‐phenylenevinylene) and Poly(lactic acid)

We report the synthesis of a series of block copolymers consisting of a rod‐like semiconducting poly(2,5‐di(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (DEH‐PPV) block and a flexible poly(lactic acid) (PLA) block that can be selectively degraded under mild conditions. Such selectively degradable block copolymers are designed as self‐assembling templates for bulk heterojunction donor–acceptor layers in organic solar cells. A lamellar microphase‐separated domain structure was identified for block copolymers with PLA volume fractions between 29 and 79% in bulk and thin films using SAXS, TEM, and AFM. Depending on the ratio of the two blocks we find either lamellae oriented parallel or perpendicular to the substrate in thin films.

     

Stereoselective Interaction between Isotactic and Optically Active Poly(lactic acid) and Phenyl‐Substituted Poly(lactic acid)

Isotactic and optically active poly(D ‐lactic acid) (PDLA) and phenyl‐substituted poly(lactic acid)s (Ph‐PLAs), i.e., poly(D ‐phenyllactic acid) (Ph‐PDLA) and poly(L ‐phenyllactic acid) (Ph‐PLLA), were synthesized and stereospecific interactions between the synthesized polymers were investigated by their thermal properties and crystallization behavior using differential scanning calorimetry (DSC). The DSC measurements indicated that PDLA is miscible with Ph‐PLAs and that the attractive interaction between PDLA and L ‐configured Ph‐PLA is higher than that between PDLA and D ‐configured Ph‐PDLA. In other words, the latter result means that poly(lactic acid) (PLA) has a higher stereoselective attractive interaction with Ph‐PLA with the reverse configuration than with Ph‐PLA of the same configuration. These results strongly suggest that PLA‐based materials with a wide variety of physical properties and biodegradability can be fabricated by blending them with substituted PLAs with the reverse and same configurations.

     

Chitosan‐Hydroxybenzotriazole Aqueous Solution: A Novel Water‐Based System for Chitosan Functionalization

Summary: A chitosan‐hydroxybenzotriazole (HOBt) aqueous solution prepared by simply mixing chitosan and HOBt in water provides an effective system to functionalize chitosan in an aqueous environment. This aqueous solution in combination with water‐soluble carbodiimide (WSC) allows the conjugation of functional groups onto chitosan under mild conditions without requiring any organic solvents or acid and heat. In this contribution, a series of model reactions that use a novel water‐based system of chitosan to functionalize the polymer with boc‐L ‐phenylalanine, poly(ethylene glycol) methyl ether, and dicarboxylated poly(ethylene glycol) is demonstrated.

Chitosan‐HOBt is effectively conjugated with R‐COOH via a water‐soluble carbodiimide (WSC) conjugating agent.     

Organosilicon‐Assisted Transformation of Living Anionic into Living Cationic Polymerization

A novel method is described for transforming an anionic polymerization process into a cationic polymerization process assisted by organosilyl groups. The reaction of the p‐tolyldimethylsilyl end group of polystyrene and trifluoromethanesulfonic acid produced a silyl triflate end group that served as a macroinitiator for the living cationic polymerization of isobutyl vinyl ether. The Si O linkage in the block copolymers underwent specific cleavage by reaction with tetrabutylammonium fluoride.

     

Step‐by‐Step Synthesis of Monodisperse Methacrylamidoalkyl Oligolactates

Summary: This paper describes the facile step‐by‐step synthesis to graft lactic acid or lactoyl lactate onto primary as well as secondary alcohol derivatives of methacrylamides via esterification. Elongation of the chains is achieved by repeating the coupling reactions with either hydroxyl‐protected monolactate or hydroxyl‐protected dilactate, followed by mild deprotection using tetrabutylammonium fluoride. This versatile synthesis route generates, on a multi‐gram scale, monodisperse oligolactates of predetermined lengths with functional end groups. The products can be used, for example, as building blocks for biodegradable polymeric materials.

The synthesis of monodisperse oligo(lactic acids) with methacrylamide end groups and a predefined number of lactic acid units.     

Synthesis of Novel Biomimetic Zwitterionic Phosphorylcholine‐Bound Chitosan Derivative

Summary: Water‐soluble biomimetic chitosan derivative conjugating zwitterionic phosphorylcholine was efficiently prepared through Atherton‐Todd reaction under the mild conditions, and the possible formation mechanism of zwitterionic product was related to the nucleophilic attack of adjacent 3‐hydroxyl on the D ‐glucosamine residue to phosphorus with the help of base. UV absorption and melting behaviors of DNA/phosphorylcholine‐bound chitosan derivative showed that the phosphorylcholine‐bound chitosan derivative could be a new carrier for long‐circulating macromolecular drug delivery.

Structure of zwitterionic PC‐chitosan.     

Automated Parallel Synthesis of MADIX (Co)Polymers

An automated parallel synthetic approach has been developed for synthesizing polymer libraries by the Macromolecular Design via the Interchange of Xanthates (MADIX) process. The experimental set‐up, parallel polymerizations, characterization, and reproducibility tests are detailed. Examples of acrylic diblock copolymers synthesized in this way are given.

Automated MADIX polymerizations of BA in the presence of a X₁ ‐capped PEA.     

Investigation on RAFT Polymerization of a Y‐Shaped Amphiphilic Fluorinated Monomer and Anti‐Fog and Oil‐Repellent Properties of the Polymers

A Y‐shaped amphiphilic fluorinated monomer, 1‐(1H,1H,2H,2H‐perfluorodecyloxy)‐3‐(3,6,9‐trioxadecyloxy)‐propan‐2‐yl acrylate has been synthesized and its polymerization by reversible addition–fragmentation chain transfer (RAFT) homopolymerization has been investigated. The results show that the molecular weights of the polymers are controlled and all the molecular weight distributions are lower than 1.4. Well‐defined copolymers with 2‐(N,N‐dimethylamino)ethyl methacrylate have been prepared by RAFT polymerization, and the surface properties of the block and random copolymers have been examined by contact angle measurement for water and hexadecane. It has been found that the surfaces of the block copolymers simultaneously exhibit excellent anti‐fog and oil‐repellent properties.

     

Bioresorbable Hydrogels Prepared Through Stereocomplexation between Poly(L‐lactide) and Poly(D‐lactide) Blocks Attached to Poly(ethylene glycol)

Block copolymers were synthesized by ring‐opening polymerization of L ‐lactide or D ‐lactide in the presence of mono‐ or dihydroxyl poly(ethylene glycol), using zinc metal as catalyst. The resulting copolymers were characterized by various techniques, namely ¹H NMR spectroscopy, differential scanning calorimetry (DSC), X‐ray diffractometry, and Raman spectrometry. The composition of the copolymers was designed such that they were water soluble. Bioresorbable hydrogels were prepared from aqueous solutions containing both poly(L ‐lactide)/poly(ethylene glycol) and poly(D ‐lactide)/poly(ethylene glycol) block copolymers. Rheological studies confirmed the formation of hydrogels resulting from stereocomplexation between poly(L ‐lactide) and poly(D ‐lactide) blocks.

Ring‐opening polymerization of L (D )‐lactide in the presence of dihydroxyl PEG using zinc powder as catalyst.     

Linear Azo Polymer Containing Conjugated 5,5′‐Azodisalicylic Acid Segments in the Main Chain: Synthesis,Characterization, and Degradation

Summary: Copolymers of poly(ethylene oxide) (PEO) and 5,5′‐azodisalicylic acid (Olsalazine, OLZ) were synthesized and evaluated by hydrolysis and in‐vitro biodegradation with azoreductase. It was found that changing the molecular weight of the PEO blocks affected the loading ratio of OLZ, and resulted in significant differences in the hydration and degradability of the copolymers. These novel azo‐containing copolymers can be used in colon‐specific drug delivery.

Release of 5‐ASA from OLZ and PEO‐OLZ copolymers incubated with rat cecum content in the presence of benzyl viologen and α‐D ‐glucose.     

Novel Biodegradable Copolymers with a Periodic Sequence Structure Derived from Succinate Butan‐1,4‐diol,and Butan‐1,4‐diamine

Summary: Novel biodegradable copolymers derived from succinate, butan‐1,4‐diol, and butan‐1,4‐diamine were synthesized by two‐step polycondensation reactions. The obtained copolymers had a periodical‐sequence structure consisting of ester and amide units, and the melting temperatures of the periodic copolymers increased with an increase in amide content. The crystalline structure of the periodic copolymers differs from that of butylene succinate homopolymer (PBS), and these results suggest that the periodically introduced amide units are included in the crystalline phase forming a novel crystalline structure.

Periodic copolyester‐amides derived from succinate, butane‐1,4‐diol, and butan‐1,4‐diamine     

Chain Walking Ethylene Copolymerization with an ATRP Inimer for One‐Pot Synthesis of Hyperbranched Polyethylenes Tethered with ATRP Initiating Sites

A one‐pot procedure for the synthesis of hyperbranched polyethylenes tethered with ATRP initiating sites by chain walking ethylene copolymerization with an acrylate‐type ATRP inimer, 2‐(2‐bromoisobutyryloxy) ethyl acrylate (BIEA) is reported. Because of its ability to incorporate acrylate‐type comonomers and tolerance toward the α‐bromoester group, the chain walking Pd‐diimine catalyst, [(ArNC(Me) (Me)CNAr)Pd(CH₃)(NCMe)]SbF₆ (Ar = 2,6‐(iPr)₂C₆H₃), allowed the successful synthesis of a series of hyperbranched copolymers tethered with 2‐bromoisobutyryl groups at different densities. These copolymers may serve as polyfunctional macroinitiators for the ATRP of functional monomers to further synthesize core‐shell structured functionalized copolymers with a hyperbranched polyethylene core grafted with side chains of the functional monomers.

     

Formation of Polyolefin‐block‐polystyrene Block Copolymers on Phenoxyimine Catalysts

Summary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation.

     

Influence of the Position of the Connecting Spacer of the Chromophore on the Nonlinear Optical Response

A new chromophore, C1 , based on a similar DπA‐structure as in the FTC ‐chromophore but with a hydroxyalkyl spacer perpendicular to the direction of the dipole moment was synthesized. Both chromophores and the CLD ‐chromophore were used to prepare high T_g nonlinear optical vinyl polymers. The influence of the position of the spacer on the DπA‐system on the NLO response of the resulting polymers was investigated.

     

Sensing Behavior of Fluorescent Cyclodextrin/Peptide Hybrids Bearing a Macrocyclic Metal Complex

Two kinds of cyclodextrin/peptide (CD/peptide) hybrids bearing Zn^II‐cyclen or cyclen, dansyl and β‐cyclodextrin (β‐CD) units have been synthesized as chemosensors for organic anionic molecules. Zn^II‐cyclen serves as a ligand site and β‐CD is a receptor site for guest molecules, while the dansyl unit acts as a fluorescent probe. Examination of the fluorescence behaviors of these CD/peptides suggest that the hybrid containing Zn²⁺ has larger binding constants with respect to anionic molecules than that without Zn²⁺.

     

A Catalytic Approach to Functional Poly(1,4‐ketone)s Bearing Pendant Monosaccharide Fragments

Summary: Novel alternating polyketone‐based polymers bearing pendant saccharide units that are accessible by polymerization catalysis are presented. The materials were synthesized by polymerization of carbon monoxide and α‐olefins containing protected glucose or N‐acetyl glucosamine residues. The dicationic Pd^II bis(phoshine) complex [Pd(dppp)(NCCH₃)₂](BF₄)₂ was used as a catalyst precursor. An O‐deacetylation of the copolymers afforded materials with amphiphilic character.

Structure of the poly(1,4‐ketone) copolymers synthesized here.     

Use of the Interpolyelectrolyte Complexes of Poly(acrylic acid)‐Chitosan as Inductors of Tolerance Against Pathogenic Fungi in Tomato (Lycopersicon esculentum Mill. var. Floradade)

The interpolyelectrolyte complexes of poly(acrylic acid)‐chitosan were investigated as inductor of systemic resistance potentially useful in the organic production of vegetables. These complexes, which are water soluble, were tested in tomato (Lycopersicon esculentum Mill. var. Floradade). The seed treatments were carried out using solutions consisting of 0.1 vol.‐% of the complex and 5 g · L^?1 NaCl in water. The data showed that this treatment produced a higher resistance to the attack by Fusarium oxysporum and Phytophthora capsici pathogens in tomato seedlings.

Formation of the interpolyelectrolyte complex of poly(acrylic acid) and chitosan.     

Self‐Assembled Micelles Based on PEG‐Polypeptide Hybrid Copolymers for Drug Delivery

A series of amphiphilic poly(L ‐leucine)‐block‐poly(ethylene glycol)‐block‐poly(L ‐leucine) (PLL‐PEG‐PLL) hybrid triblock copolymers have been synthesized. All the blocks in this system have good biocompatibility and low toxicity. The PLL‐PEG‐PLL copolymers could self‐assemble into micelles with PLL blocks as the hydrophobic core and PEG blocks as the hydrophilic shell, which were characterized by FT‐IR, ¹H NMR, and transmission electron microscopy analysis. The critical micellar concentration of the copolymer was 95.0 mg · L⁻¹. The circular dichroism spectrum shows that the PLL segments adopt a unique α‐helical conformation, which is found to play an important role in controlling the drug release rate. The drug release could be effectively sustained by encapsulation in the micelles. The copolymers may have potential applications in drug delivery.