It's a subtle difference. "Expectations for" are more like "hopes" not necessarily directed toward the subject. "My expectation for the weekend is that it will be sunny." "My expectations for my children are only that they will be happy." "Expectation of" sounds more like the subject wants something from something/or someone. "The new employee did not fulfill the expectations I had of her." "His expectations of me were unreasonable." [He expected me to do too much for him]. If I expect that John will produce something that will benefit me, I might say, "I have high expectations of John." If I think John will produce something for himself, I might say, "I have a high exceptions for John."