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The radical polymerization of multivinyl monomers usually provides crosslinking polymers. It is a significant challenge how to control the structure of the polymers and to obtain soluble polymers in a high yield. In this work, the radical branching polymerizations of two asymmetrical divinyl monomers, allyl methacrylate (AMA) and furfuryl methacrylate (FMA), were investigated in detail. Both of the reactivity of the bonds and the weak transfer of isopropyl alcohol (IPA) were used to control the development of branching polymerizations and avoid gelation, without any other additives. As a result, the soluble branched PAMAs and PFMAs with extremely high molecular weights (106∼107) were successfully obtained. The branching factor (g’) of PAMA is very low (0.01–0.02), and that of PFMA is the higher (about 0.3) due to the weaker reactivity of furfuryl groups. Comparing with the results of using thiol chain transfer agent, the chain transfer of IPA had no obvious influence on the chain propagation at the early stage of the polymerizations, but could delay the gelation successfully at the later stage. Furthermore, the development of the branching structure could be studied in detail on the branching factor and rms radius since the gelation process was extended from several minutes to several hours.

Aliphatic polyesters have been widely used in environmental and biomedical engineering, but a lack of functional groups limits their applications. Here, we reported a facile approach to synthesize vinyl functional polyester via the ring opening copolymerization of e-caprolactone (CL) and allyl glycidyl ether (AGE). NMR analysis confirmed the copolymeric structures and suggested that the copolymerization depended on the epoxide ring of AGE rather than vinyl group. The amount of AGE incorporated into the copolymers (FAGE) increased with the amount of epoxide monomer feed with a maximum incorporation of 16.7%. Increasing temperature helped AGE to incorporate into the copolymer, however, accompanying with lots amount of AGE homopolymers. The resulting copolymer was successfully post-functionalized by thiol-end click, epoxidation, and bromination reactions depending on the reactivity of pendent ally groups. This facile and efficient approach can be used to functionalize biodegradable polymers and synthesize some new polymers under mild conditions.

It is believed that polymer chains mainly terminate through bimolecular termination in free-radical polymerization, however, there is few convincing evidence to support it. In benzoyl peroxide (BPO) initiated styrene free-radical polymerization, our studies demonstrate that polymer chain terminates dominantly through primary radical termination rather than by bimolecular termination as described in polymer textbooks. Even at very high primary radical concentration or at very low monomer concentration, primary radical termination still dominates (FPRT&CTI>70%) besides the occurrence of some bimolecular coupling terminations. Two kinds of model polymers were prepared, one for bimolecular coupling termination, and the other for primary radical termination. The 1H-, 13C-, DEPT135-, and 2D HSQC NMR spectra of the polystyrene initiated by BPO are almost the same as those of the model polystyrene for primary radical termination, but they are quite different from those of the model polystyrene for bimolecular coupling termination, demonstrating directly that primary radical termination rather than bimolecular coupling termination dominates in BPO-initiated styrene free-radical polymerization.

Both temperature and light stimuli-responsive 4-propoxyazobenzene-terminated poly( N -isopropylacrylamide)s (PNIPAMs) were successfully synthesized by the atom transfer radical polymerization (ATRP) of NIPAM. 1 H NMR and UV– vis absorption spectra indicated rapid photoisomerization rate of 4-propoxyazobenzene moiety. Interestingly, the lower critical solution temperature (LCST) for PNIPAM aqueous solution clearly decreased after UV irradiation, and the repeated LCST difference (ΔT maxy = 5 °C) depended on both the number-average molecular weight and amount of azobenzene chromophore. Dynamic light scattering (DLS) and static light scattering (SLS) measurements showed that the PNIPAM aqueous solution could self-assemble into nano-micelles with 4-propoxyazobenzene as the hydrophobic cores and PNIPAM chains as the hydrophilic shells. UV irradiation induced the increase of particle size due to the formation of much looser cores of cis -azobenzene. TEM images showed the presence of both nanorods and spherical micelles. After UV irradiation, the unstable spherical micelles transformed to metastable nanorods, then to longer rods, and finally the longer rods began to transform to flake-like particles via horizontal inter-rod aggregation above LCST.

Vinyl-functionalized hyperbranched polymers (HBPs) have attracted much attraction because their pendant vinyl groups can be further modified for a required application. However, the syntheses of these polymers are difficult, because the cross-linking is inevitable during the polymerization reaction. The present work reports a new, facile, one-step strategy for the synthesis of vinyl-functionalized HBPs via the self-condensing anionic copolymerization of commercially available allyl methacrylate and hydroxyethyl methacrylate with a monomer conversion approaching 100% at room temperature. The hyperbranched structures were confirmed by triple-detection size exclusion chromatography. The pendent vinyl groups of the resulting polymer were successfully modified by a “thiol-ene” reaction. This method provides a facile approach for preparing vinyl-functionalized HBPs with excellent monomer conversions under mild conditions, and will be useful in materials chemistry.

The development of networks and structural heterogeneity in the atom transfer radical polymerization (ATRP) of dimethacrylates was studied. The structural and kinetic evolutions during the polymerization were followed using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and extraction/swelling measurement. The reversible activation/deactivation equilibrium between growing radical and dormant species slowed down the polymerization process, giving rise to sufficient chain relaxation and diffusion of reactive species, which favored the formation of homogeneous networks. Compared to the networks prepared by conventional free radical polymerization that favored microgel formation, the ATRP products were more homogeneous, suggested by narrower peak width of the tan δ curve. It was also found that crosslinking density and degree of structural heterogeneity of the ATRP products increased with vinyl conversion. The loss of the living feature at high conversions did not further increase the structural heterogeneity. The ATRP of dimethacrylates with longer spacer yielded more homogeneous networks with lower crosslinking density and lower glass transition temperature.

An approach to enhancing the volumetric expansion on polymerization of spirobislactone is proposed. This approach suggests a molecular modification of spirobislactone through attaching a rigid pendant segment bearing maleimido group to its aromatic ring. An additional volumetric expansion is achieved from loose molecular packing in cured resins due to the steric hindrance effect among rigid pendent segments. Thus a new monomer, maleimido-functionalized spirobislactone (MFS), is prepared. In order to evaluate the volumetric expansion of MFS during curing, tetraglycidyl 4,4′-diamino diphenyl methane (TGDDM) is employed to cure with MFS. The volumetric expansion of MFS on curing is measured to be 12.3%, higher than that of net spirobislactone monomer. The existence of loose molecular packing in MFS/epoxy cured resins is demonstrated by morphology observation of the cured resin stained by the phosphotungstic acid (PTA), and the stained regions are observed to be nanoparticles. Such a cured resin, prepared from 20 mol% of MFS and 80 mol% of TGDDM epoxy resin, shows excellent toughness (Charpy impact strength 13,000 J/m2) and good mechanical strength (flexural strength 120 MPa, storage flexural modulus 4.2 GPa). Its glass transition temperature by dynamic mechanical thermal analysis (DMA) attains 227 °C, much higher than that of the cured resin from net spirobislactone and epoxy resin.