Use of a semifluorinated acrylic compound in reinforcement of high density polyethylene and some microsphere preparation studies

In this dissertation, a novel semifluorinated acrylic compound, 3,3,4,4,5,5,6,6,7,7,8,8,8-dodecafluoro-5-methyloctyl-4-(acryloyloxy) benzoate (ABCF13) was synthesized, and it was used in the reinforcement of high density polyethylene (HDPE) by graft copolymerization and in the preparation of crosslinked microspheres by suspension polymerization. The prepared microspheres were then used in the preparation of blends with HDPE. The thermal, microstructural, mechanical and morphological properties of all the graft coproducts and the blends were investigated. The monomer, ABCF13 was synthesized by the reaction of 3,3,4,4,5,5,6,6,7,7,8,8,8-dodecafluoro-1-octanol with p-acryloyloxybenzoyl chloride (ABC) in ethyl acetate containing triethylamine. ABC was precedingly synthesized by refluxing p-acryloxyloxybenzoic acid, prepared by the reaction of acryloylchloride with p-hydroxybenzoic acid in basic medium, in thionly chloride. The graft copolymerization of ABCF13 onto the HDPE was conducted by bulk-melt polymerization at 140°C by using benzoyl peroxide initiator in evacuated tubes. The products involving poly(ABCF13) units at varying percentages were prepared by employing ABCF13 at the concentrations of 5, 10, 15, 20, 30 and 40% in the reaction mixtures. The content of poly(ABCF13) in the products and percent conversion of the reactions were determined gravimetrically. The percent conversion exhibited consistent rise with the increase of monomer concentration in the reaction mixture and reached the maximum value, 97.9% at 40% ABCF13 yielding the product including 39.18% poly(ABCF13). The DSC analyses of the coproducts displayed that there existed considerable and significant increases in both the melting temperature of crystalline domains and crystallinity in the HDPE matrix, consistent with the graft content. Maximum melting temperature 134.2°C was recorded with 13.96% poly(ABCF13), which was followed by decreases with the increasing of content. The XRD analyses revealed that the graft copolymerization gave rise to significant expansions in lateral dimensions of orthorhombic unit cells in crystalline domains of HDPE. The maxima, 7.420 Å in the parameter a (0.84% increase) and 4,957 Å in the parameter b (0.98% increase) were recorded with the product again involving 13.96% poly(ABCF13). The maxima were then followed by contractions. The parameter c, however, remained relatively unchanged. The grain (crystal) size increased initially, and after reaching maximum at 9.15% poly(ABCF13) reduced gradually with the content to sizes even smaller than that of pure HDPE. The PALS analyses showed that the size of the free volumes increased almost linearly with the percentage of poly(ABCF13) while the free volume fraction in the products exhibited a decrease tendency with the content. Remarkable improvements were achieved in the mechanical behaviors of the products. The maximum tensile strength 43.75 MPa and elastic modulus 393 MPa (133% and 9% improvement, respectively) were achieved with the product comprising 9.15% poly(ABCF13). Moreover, the absorbed energy in the impact tests exhibited 100% increase in the same product. The SEM images of the tensile and impact fractured surfaces of the products showed that the samples possessed completely homogeneous structure without any phase separation. A gradual transition from ductile behavior to brittle nature was observed as poly(ABCF13) percentage increased in the matrix. The well-shaped, crosslinked poly(ABCF13) microspheres with the size in the range of 10-100 µm were prepared by using ethylene glycol dimethacrylate (1%) (crosslinking agent), potassium persulfate (1.3%) (water soluble initiator), 0.2 g ABCF13 monomer in 150 mL of water at 70°C for 24 h reaction time and with the stirring rate of 500 rpm. Structure and morphology of the products were monitored by SEM. The poly(ABCF13) microsphere-HDPE blends involving the microspheres at varying ratios (1, 3, 5, 7 and 10%) were prepared by direct mixing of the components, and molded by microinjection molding for characterizations. The processing with the microspheres led to decrease in the melting temperature of HDPE in consistence with the content of microsphere. The a and b unit cell parameters increased initially and reached maxima with the sample including 5% microsphere, which were followed by dramatic decreases. The c parameter remained relatively unchanged. The mechanical tests of the products displayed that there existed considerable improvements in tensile strength, modulus and impact strength. The maximum tensile strength 25.66 MPa, elastic modulus 499 MPa and maximum absorbed energy in the impact test 26.84 kJ/m2 (29%, 42% and 41% improvement, respectively) were achieved with the blend involving 5% microsphere. After the maxima, the mechanical characters depicted weakening trend as the microsphere content increased in the matrix. The SEM analyses revealed that although there existed fibrillar formations in all samples, the extensions decreased with the increase of the microsphere content. While ductile behavior was observed with the formation of long-bulky extensions at low contents, brittleness started to prevail at high contents with some short and thin fibrils